Apical CI/OH-/HCO3-exchanger in kidney and GI tract

肾脏近端小管和胃肠道的顶端氯/碱交换器与NHE3平行工作，对氯的吸收和液体的动态平衡是必不可少的。然而，关于这种交换器的分子特性和主要作用模式，人们知之甚少。SLC26A6，也被称为PAT1或CFEX，是一个高度保守的离子转运蛋白家族(命名为SLC26a)的成员，其中许多介导阴离子交换。SLC26A6可介导CI‘/HCO3-、Cl/甲酸和Cl-/草酸交换，是近曲小管顶端氯/碱交换的理想候选者。我们的实验证明，SLC26A6介导CI-/HCO3-交换，位于胃壁细胞近端小管、小肠和小管小管的顶膜上，并被天然的NH4+上调。 发生在肾脏、近端小管和小肠的化学物质。我们进一步证明，在大鼠和小鼠分离的微灌流近端小管和胃壁细胞的小管囊中存在顶端CI/HCO3-交换。我们推测SLC26A6是肾脏近端小管和十二指肠的主要顶端阴离子交换器，在生理条件下主要作为CI-/HCO3-交换器发挥作用，是氯离子吸收的主要原因。在胃中，PAT1可能是在静止状态下中和含有H-K-ATPase的囊泡的腔酸性所必需的。当前的目的是 建议确定顶端CI-/IHCO3-交换器和PAT1(SLC26A6)在肾脏近端小管和胃肠道对氯(和液体)吸收中的作用。为此，我们建议：1.确定在模拟近端小管环境的溶液存在的情况下，离体微灌流近端小管中顶端CI/HCO3-交换器的特性，并确定其在氯离子重吸收中的作用；2.利用SLC26A6(PAT1)缺失的小鼠，确定SLC26A6在顶端Cltbase交换和肾近端小管重吸收中的作用；3.检测SLC26A6(PAT1)和肾脏近端小管顶端CI/HCO3-交换器的急性和慢性调节；4.确定SLC26A6在胃肠功能、肾脏近端小管功能中的作用 包括CI的吸收和对十二指肠酸损伤和胃酸分泌的保护，使用SLC26A6基因缺失的小鼠。深入了解生理状态下肾脏近端小管和上胃肠道的PAT1和顶端CI-/HCO3-交换的功能和分子特性，以及对PAT1缺陷小鼠的检查，将大大加深我们对上皮组织顶端CI-/碱基交换和cr吸收的理解。他们应该进一步促进未来对这种转运蛋白在影响电解质和酸碱平衡的病理生理状态中的作用的研究。

The apical chloride/base exchanger in kidney proximal tubule and gastrointestinal tract works in parallel with NHE3 and is essential for chloride absorption and fluid homeostasis. However, less is known about the molecular identity and the main functional mode of this exchanger. SLC26A6, also known as PAT1 or CFEX, is a member of a large, highly conserved family of ion transporters (designated as SLC26A) many of which mediate anion exchange. SLC26A6 can mediate CI'/HCO3-, Cl/formate and Cl-/oxalate exchanges, indicating that it is an ideal candidate for apical Cl/base exchange in proximal tubule. Our experiments demonstrate that SLC26A6 mediates CI-/HCO3- exchange, is located on the apical membrane of proximal tubule, small intestine and tubulovesicles of gastric parietal cells, and is upregulated by NH4+, a naturally occurring chemical in kidney proximal tubule and small intestine. We further demonstrate the presence of an apical CI/HCO3- exchange in rat and mouse isolated microperfused proximal tubules and in tubulovesicles of gastric parietal cells. We hypothesize that SLC26A6 is the main apical anion exchanger in kidney proximal tubule and duodenum, functions predominantly as a CI-/HCO3- exchanger under physiologic conditions and is responsible for the bulk of chloride absorption. In the stomach, PAT1 may be essential for neutralizing the luminal acidity of H-K-ATPase-containing vesicles during the resting state. The purpose of the current proposal is to ascertain the role of the apical CI-/IHCO3- exchanger and PAT1 (SLC26A6) in chloride (and fluid) absorption in kidney proximal tubule and gastrointestinal tract. Toward this end, we propose to: 1. Characterize the apical CI/HCO3- exchanger in isolated microperfused proximal tubule and ascertain its role in chloride reabsorption in the presence of solutions mimicking proximal tubule milieu, 2. Ascertain the role of SLC26A6 in apical Cltbase exchange and cr reabsorption in kidney proximal tubules using SLC26A6 (PAT1) null mice, 3. Examine the acute and chronic regulation of SLC26A6 (PAT1) and apical CI-/HCO3- exchanger in kidney proximal tubule, and 4. Determine the role of SLC26A6 in gastric and intestinal function, including CI absorption and protection against acid injury in the duodenum and acid secretion in the stomach, using SLC26A6 null mice. Insight into the functional and molecular properties of PAT1 and apical CI-/HCO3- exchange in kidney proximal tubule and upper gastrointestinal tract in physiologic states and examination of PAT1 deficient mice should significantly enhance our understanding regarding the apical CI-/base exchanger and cr absorption in epithelial tissues. They should further facilitate future investigations into the role of this transporter in pathophysiologic states affecting electrolyte and acid-base homeostasis.